1. Field of the Invention
The present invention relates generally to satellite quadrature phase shift keyed (QPSK) transmission systems, and more specifically to phase error correction for correcting phase errors introduced to the QPSK signal during transmission.
2. Description of the Related Art
In satellite communication systems using QPSK modulation, P-channel and Q-channel unique words (or burst code words) are inserted in a preamble of each burst transmission for purposes of frame, or burst synchronization. During transmission, signals will suffer undesirable effects and as a result phase errors such as bit reversals and channel reversals can occur.
According to prior art phase error cancellers, the QPSK signal is converted to P-channel and Q-channel baseband signals, and the N bits of the P-channel unique word is compared with N bits of possible bit patterns which the transmitted P-channel unique word may assume during transmission, and mismatches are detected between them to produce a mismatch count. The mismatch count is then evaluated against thresholds to generate an error correcting signal. However, the current technique is not satisfactory for precisely correcting possible phase errors and improvement has been desired.